NATO is concerned about support Russia could provide for North Korea's missile and nuclear programmes, the alliance's head said on Tuesday as Russian President Vladimir Putin began his first trip to the reclusive nuclear-armed country in 24 years.

Putin, on a state visit for talks with North Korean leader Kim Jong Un, vowed to deepen trade and security ties and to support the North against the US, a close ally of its bitter rival South Korea.

The US has accused North Korea of supplying "dozens of ballistic missiles and over 11,000 containers of munitions to Russia" for use in Ukraine.

NATO Secretary-General Jens Stoltenberg told a joint press briefing after talks with US Secretary of State Antony Blinken that Russia's war in Ukraine was being propped up by China, North Korea and Iran, who all wanted to see the Western alliance fail.

"We are of course also concerned about the potential support that Russia provides to North Korea when it comes to supporting their missile and nuclear programmes," Stoltenberg said.

He said this and China's support for Russia's war economy showed how security challenges in Europe were linked to Asia and added that next month's NATO summit in Washington would see a further strengthening of the alliance's partnerships with Australia, New Zealand, South Korea and Japan.

Stoltenberg said there needed to be "consequences" at some stage for China.

"They cannot continue to have normal trade relationships with countries in Europe and at the same time fuel the biggest war we have seen in Europe since the Second World War," he said.

Stoltenberg said it was too early to say what those consequences might be, "but it has to be an issue that we need to address because to continue as we do today is not viable."

On Monday, White House National Security spokesperson John Kirby said Washington was watching the North Korea-Russia relationship "very, very closely" as there "could be some reciprocity ... that could affect security on the Korean Peninsula."

On Tuesday, White House spokesperson Karine Jean-Pierre told a news briefing that deepening Russia-North Korea cooperation was "a trend that should be of great concern to anyone interested in maintaining peace and stability in the Korean Peninsula."

She noted that a statement from Putin and Chinese leader Xi Jinping from a May summit had stressed political and diplomatic means as the only way to resolve the Korean issue, and added: "We hope this is a message that Putin will convey to Kim in their discussion."

At the briefing with Stoltenberg, Blinken said Putin's Pyongyang trip was a sign of his "desperation" to strengthen relations with countries that can support his war in Ukraine.

He added that China's support had enabled Russia to maintain its defense industrial base, supplying 70% of Moscow's machine tool imports and 90% of the microelectronics. "That has to stop," he said.

Last week, US Deputy Secretary of State Kurt Campbell said Washington was concerned by what Russia would give North Korea in return for weapons Pyongyang has supplied.

"Hard currency? Is it energy? Is it capabilities that allow them to advance their nuclear or missile products? We don't know. But we're concerned by that and watching carefully," he said.

The top US arms control official, Under Secretary of State Bonnie Jenkins, has said she believes North Korea is keen to acquire fighter aircraft, surface-to-air missiles, armoured vehicles, ballistic missile production equipment or materials, and other advanced technologies from Russia.